Pulp is treated in a dispersing device where the impurities of the pulp are separated from the fibers that are nevertheless not damaged in the treatment. This may be accomplished with the aid of mutually opposed blade equipped blade surfaces of the dispersing device where one blade surface along its base (stator) is fixed and the other blade surface along its base (rotor) is rotating in relation to the other blade surface. The blades and the narrow openings between them cause the pulp to move back and forth in the dispersing device, whereby separation of impurities from the fibers is accomplished. The purpose of dispersing is usually mechanical release of impurities from the fibers and simultaneously the grinding of impurities into smaller particles without nevertheless negatively affecting the properties of the fibers.
A dispersing device is especially well suited for treatment of pulp mass containing waste paper that contains ink particles or impurities such as adhesives and melt or fusion coatings. A method and dispersing device intended to treat this kind of pulp is presented in Patent Publication SE 502906. In the publication there is presented a grinding element that consists of two mutually opposed grinding disks that are equipped with elevated indents. The inclined elevated patterns are arranged radially on the disks.
In addition to the planar dispersing devices even cone-shaped dispersing devices may be used. However, the problem with the conical dispersing devices is the small amount of mass transferring power allowed by them. Therefore when the pressure in the outlet chamber is high, that is, in the openings between the indents, the thrust is high, and adjusting the working faces becomes more difficult and the load of the dispersing device increases. The dispersing device may even become clogged, whereby the process in interrupted. This problem is avoided by using the inventive method.